Botkin Environmental Science Earth as Living Planet 8th txtbk

Reexamining Themes and Issues 167
The competitive exclusion principle states that two species
that have exactly the same requirements cannot coexist
in exactly the same habitat; one must win. The
reason more species do not die out from competition
is that they have developed a particular niche and thus
avoid competition.
The number of species in a given habitat is determined by
many factors, including latitude, elevation, topography, severity
of the environment, and diversity of the habitat. Predation
and moderate disturbances, such as fire, can actually
increase the diversity of species. The number of species also
varies over time. Of course, people affect diversity as well.
REEXAMINING THEMES AND ISSUES
Human
Population
Sustainability
Global
Perspective
Urban World
People
and Nature
Science
and Values
The growth of human populations has decreased biological diversity. If
the human population continues to grow, pressures will continue on endangered
species, and maintaining existing biological diversity will be an
ever-greater challenge.
Sustainability involves more than just having many individuals of a species.
For a species to persist, its habitat must be in good condition and
must provide that species’ life requirements. A diversity of habitats enables
more species to persist.
For several billion years, life has affected the environment on a global
scale. These global effects have in turn affected biological diversity. Life
added oxygen to the atmosphere and removed carbon dioxide, thereby
making animal life possible.
People have rarely thought about cities as having any beneficial effects
on biological diversity. However, in recent years there has been a growing
realization that cities can contribute in important ways to the conservation
of biological diversity. This topic will be discussed in Chapter 22.
People have always treasured the diversity of life, but we have been one of
the main causes of the loss in diversity.
Perhaps no environmental issue causes more debate, is more central to arguments
over values, or has greater emotional importance to people than
biological diversity. Concern about specific endangered species has been
at the heart of many political controversies. Resolving these conflicts and
debates will require a clear understanding of the values at issue, as well as
knowledge about species and their habitat requirements and the role of
biological diversity in life’s history on Earth.